PIC17C756A MICROCHIP [Microchip Technology], PIC17C756A Datasheet - Page 62

• Manufacturer Part Number: PIC17C756A
• Description: High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

PIC17C7XX
8.2
Table writes to external memory are always two-cycle
instructions. The second cycle writes the data to the
external memory location. The sequence of events for
an external memory write are the same for an internal
write.
8.2.1
The “i” operand of the TABLWT instruction can specify
that the value in the 16-bit TBLPTR register is automat-
ically incremented (for the next write). In Example 8-1,
the TBLPTR register is not automatically incremented.
FIGURE 8-5:
DS30289B-page 62
Table Writes to External Memory
Note: If external write and GLINTD = ’1’ and Enable bit = ’1’, then when ’1’
TABLE WRITE CODE
The highest pending interrupt is cleared.
AD15:AD0
Instruction
Instruction
Executed
Fetched
TABLWT WRITE TIMING (EXTERNAL MEMORY)
ALE
WR
OE
OE
Q1 Q2 Q3 Q4
’1’
INST (PC-1)
TABLWT
PC
Q1 Q2 Q3 Q4
TABLWT cycle1
INST (PC+1)
PC+1
EXAMPLE 8-1:
CLRWDT
MOVLW
MOVWF
MOVLW
MOVWF
MOVLW
TLWT
MOVLW
TABLWT
Data write cycle
Q1 Q2 Q3 Q4
TABLWT cycle2
TBL
HIGH (TBL_ADDR) ; Load the Table
TBLPTRH
LOW (TBL_ADDR)
TBLPTRL
HIGH (DATA)
1, WREG
LOW (DATA)
0,0,WREG
Flag bit, do table write.
Data out
Q1 Q2 Q3 Q4
TABLE WRITE
INST (PC+2)
INST (PC+1)
2000 Microchip Technology Inc.
PC+2
;
; Clear WDT
;
;
;
; Load HI byte
;
; Load LO byte
;
;
;
program memory
address
in TABLATH
in TABLATL
and write to
(Ext. SRAM)